This invention relates generally to turbines, and more particularly, to a method and apparatus for providing regenerative turbines with augmented fluid motion in the exit portion of the turbine rotor channel.
Regenerative turbines are inherently low efficiency rotary machines, but they may be used advantageously where fluids with low flow rates and relatively high pressure ratios are available. In a regenerative turbine, regeneration takes place in the peripheral region of a rotor by radial reentry of fluid into the rotor. Regenerative turbines have best efficiency at low rotor speeds and low fluid flow speeds. The low rotor speed of this type of turbine in relation to the speed of the device being driven allows the turbine rotor shaft and the device being driven to be easily coupled, resulting in simple initial construction and increased operating reliability. The inherent low speed of regenerative turbines permits the safe operating limits of bearings and rotor components to be much lower than those of high speed turbines. For example, higher fluid tempertures, when necessary, are permitted in a regenerative turbine using a particular component than are permitted in a high speed turbine using the same component. Regenerative turbines are used where small amounts of mechanical power are extracted at low rotational speeds from high pressure or high temperature energy sources. Regenerative turbines have large flow passages and do not require critical dimensional tolerances for the components thereof. The rotor blades are simplified in construction and the rotor channels do not require vanes or blades. One or more columns of rotor blades are arranged around the circumferences of the rotor with the blade working surfaces extending parallel to the axis of the cylindrically shaped rotor body. Regenerative turbine structures are generally light in weight and simple in design resulting in economical construction costs and simplified maintenance.
As fluid flows through a regenerative turbine rotor and the channel adjacent to the rotor, the fluid flow generally traces a helical path for each column of blades. Regenerative turbines may have simplified blade structures because energy transfer between the fluid and the rotor is accomplished by frictional forces exerted by the fluid upon the rotor with the rotor being dragged along by the fluid stream. In a regenerative turbine regeneration action occurs over the rotor periphery by a mixing of the rotor fluid stream and the channel fluid streams. The fluid flow can be visualized as split into two components, a through component and a circulatory component. The circulatory component for each column of blades describes a spiral screw-like path with the fluid passing through the rotor and the adjacent channel several times. The number of fluid passes through the turbine is zero at turbine runaway conditions and increases to a maximum at stalling conditions which also produces the greatest torque.
The need has arisen in recent years for a turbine which operates effectively in naturally occurring low velocity fluid mediums such as rivers and wind streams. Improvements in regenerative turbine designs provide for extraction of greater amounts of useful energy from these virtually untapped sources of renewable energy.